Immune regulatory activities of early secreted antigenic target of 6-kD protein of Mycobacterium tuberculosis and implications for tuberculosis vaccine design

Aqueous extract-mediated green synthesis of CuO nanoparticles: Potential anti-tuberculosis agents

The emergence of drug-resistant strains in tuberculosis treatment underscores the urgency for novel therapeutic approaches. This study investigates the anti-tuberculosis activity of green-synthesized copper oxide (CuO) nanoparticles (NPs) using garlic and astragalus extracts. The physicochemical characterization of the nanoparticles confirms successful synthesis, followed by assessment of their antibacterial properties and safety profile. Rats infected with Mycobacterium tuberculosis are treated with nanocomposites derived from garlic extract at doses of 50 mg/kg and 100 mg/kg body weight. Evaluation includes the analysis of Early secreted antigenic target of 6 kDa (ESAT-6) expression and confirmation of antibodies through molecular assays. Administration of garlic and nanocomposites demonstrates significant inhibitory effects on tuberculosis progression in rats, validated by safety assessments and antibacterial efficacy. Notably, the 100 mg/kg dosage exhibits pronounced mitigation of tuberculosis-induced oxidative stress and lung damage. In conclusion, the combined administration of garlic extracts and green-synthesized nanocomposites shows promising efficacy in reducing tuberculosis infection, highlighting a potential avenue for anti-tuberculosis interventions.

Mycobacterium tuberculosis virulence protein ESAT-6 influences M1/M2 polarization and macrophage apoptosis to regulate tuberculosis progression

BACKGROUND

Tuberculosis (TB) is an infectious disease caused by infection with Mycobacterium tuberculosis (Mtb), and it remains one of the major threats to human health worldwide. To our knowledge, the polarization of M1/M2 macrophages were critical innate immune cells which play important roles in regulating the immune response during TB progression.

OBJECTIVE

We aimed to explore the potential mechanisms of M1/M2 macrophage polarization in TB development.

METHODS

THP-1 macrophages were treated with early secreted antigenic target of 6 kDa (ESAT-6) protein for an increasing time. The polarization profiles, apoptosis levels of M1 and M2 macrophages were detected by RT-qPCR, immunofluorescence, Western blot and flow cytometry.

RESULTS

ESAT-6 initially promoted the generation of pro-inflammatory M1-polarized macrophages in THP-1 cells within 24 h, which were suppressed by further ESAT-6 treatment at 30-42 h. Interestingly, ESAT-6 continuously promoted M2 polarization of THP-1 cells, thereby maintaining the anti-inflammatory response in a time-dependent manner. In addition, ESAT-6 promoted apoptotic cell death in M1-polarized macrophages, which had little effects on apoptosis of M2-phenotype of macrophages. Then, the potential underlying mechanisms were uncovered, and we verified that ESAT-6 increased the protein levels of TLR4, MyD88 and NF-κB to activate the TLR4/MyD88/NF-κB pathway within 24 h, and this signal pathway was significantly inactivated at 36 h post-treatment. Interestingly, the following experiments confirmed that ESAT-6 TLR4/MyD88/NF-κB pathway-dependently regulated M1/M2 polarization and apoptosis of macrophage in THP-1 cells.

CONCLUSION

Our study investigated the detailed effects and mechanisms of M1/M2 macrophages in regulating innate responses during TB development, which provided a new perspective on the development of treatment strategies for this disease.

Structure based design of effective HtpG-derived vaccine antigens against M. tuberculosis

Vaccine development against Tuberculosis is a strong need, given the low efficacy of the sole vaccine hitherto used, the Bacillus Calmette–Guérin (BCG) vaccine. The chaperone-like protein HtpG_Mtb of M. tuberculosis is a large dimeric and multi-domain protein with promising antigenic properties. We here used biophysical and biochemical studies to improve our understanding of the structural basis of HtpG_Mtb functional role and immunogenicity, a precious information to engineer improved antigens. We showed that HtpG_Mtb is a dimeric nucleotide-binding protein and identified the dimerisation interface on the C-terminal domain of the protein. We also showed that the most immunoreactive regions of the molecule are located on the C-terminal and middle domains of the protein, whereas no role is played by the catalytic N-terminal domain in the elicitation of the immune response. Based on these observations, we experimentally validated our predictions in mice, using a plethora of immunological assays. As an outcome, we designed vaccine antigens with enhanced biophysical properties and ease of production, albeit conserved or enhanced antigenic properties. Our results prove the efficacy of structural vaccinology approaches in improving our understanding of the structural basis of immunogenicity, a precious information to engineer more stable, homogeneous, efficiently produced, and effective vaccine antigens.

A neutrophil-based test as an auxiliary tool for substantiating the diagnosis of bovine tuberculosis

Background

Bovine tuberculosis (bTB) is still a prominent threat to animal health; lacking an efficient vaccine, other than BCG to get rid of tuberculosis, the most effective way for this is culling and slaughtering the infected animals. There are several cellular, serological, and molecular tests for the diagnosis of the disease but the most practical one at the field level is the double skin testing with bovine and aviary tuberculins. This is not a very specific test but is sensitive enough to identify most diseased animals; adjunct practical tests are desirable to strengthen the utility of skin tests. All lymphoid and myeloid cells participate, in diverse grades, in the immune response to tuberculosis with neutrophils playing an unintended pathologic role. The study aimed to investigate the response of neutrophils to agents present in the sera of tuberculous cows.

Methods

We have developed a neutrophil-based test (N BT) to identify diseased cows within a herd suspected of having tuberculosis; a positive N BT correlates with a positive double skin test. In this test, healthy neutrophils are incubated with the sera of healthy or tuberculous cows for 3 and 6 h, and the nuclear morphologic changes are recorded and analyzed.

Results

Sera from tuberculous but not from healthy cows induce nuclear alterations including pyknosis, swelling, apoptosis, and sometimes NETosis, in healthy neutrophils, and CFP 10 and ESAT 6 participate in the phenomenon.

Conclusion

We propose the N BT as an auxiliary tool for substantiating the diagnosis of bTB reinforcing the PPD test outcome to help decide whether or not a cow should be sacrificed.

The ESX-1 Virulence Factors Downregulate miR-147-3p in Mycobacterium marinum-Infected Macrophages

As important virulence factors of Mycobacterium tuberculosis, EsxA and EsxB not only play a role in phagosome rupture and M. tuberculosis cytosolic translocation but also function as modulators of host immune responses by modulating numerous microRNAs (miRNAs). Recently, we have found that mycobacterial infection downregulated miR-148a-3p (now termed miR-148) in macrophages in an ESX-1-dependent manner. The upregulation of miR-148 reduced mycobacterial intracellular survival. Here, we investigated miR-147-3p (now termed miR-147), a negative regulator of inflammatory cytokines (e.g., interleukin-6 [IL-6] and IL-10), in mycobacterial infection. We infected murine RAW264.7 macrophages with Mycobacterium marinum, a surrogate model organism for M. tuberculosis, and found that the esxBA-knockout strain (M. marinum ΔesxBA) upregulated miR-147 to a level that was significantly higher than that induced by the M. marinum wild-type (WT) strain or by the M. marinum ΔesxBA complemented strain, M. marinum ΔesxBA/pesxBA, suggesting that the ESX-1 system (potentially EsxBA and/or other codependently secreted factors) is the negative regulator of miR-147. miR-147 was also downregulated by directly incubating the macrophages with the purified recombinant EsxA or EsxB protein or the EsxBA heterodimer, which further confirms the role of the EsxBA proteins in the downregulation of miR-147. The upregulation of miR-147 inhibited the production of IL-6 and IL-10 and significantly reduced M. marinum intracellular survival. Interestingly, inhibitors of either miR-147 or miR-148 reciprocally compromised the effects of the mimics of their counterparts on M. marinum intracellular survival. This suggests that miR-147 and miR-148 share converged downstream pathways in response to mycobacterial infection, which was supported by data indicating that miR-147 upregulation inhibits the Toll-like receptor 4/NF-κB pathway.

Structural features of HtpGMtb and HtpG-ESAT6Mtb vaccine antigens against tuberculosis: Molecular determinants of antigenic synergy and cytotoxicity modulation

Vaccine development against tuberculosis is an urgent need as the only available vaccine, M. bovis Bacillus Calmette Guerin (BCG), is unable to provide significant protection in adults. Among newly identified antigens, Rv2299c is an excellent candidate for the rational design of an effective multi-antigenic TB vaccine. Also, when fused to the T cell antigen ESAT6, it becomes highly effective in boosting BCG immunization and it adopts low cytotoxicity compared to ESAT6. We here characterize these proteins by coupling various biophysical techniques to cytofluorimetry and computational studies. Altogether, our data provide an experimental evidence of the role of Rv2299c as a dimeric and highly thermostable molecular chaperone, here denoted as HtpGMtb. Molecular dynamics simulations show that ATP rigidly anchors the ATP-binding loop in a conformation incompatible with the structure of the free enzyme. We also show that HtpGMtb dimeric state is an important molecular feature for the improved antigenic and cytotoxic properties of HtpG-ESAT6Mtb. Indeed, structural features of HtpG-ESAT6Mtb show that not only does this molecule combine the antigenic properties of HtpGMtb and ESAT6, but HtpGMtb locks ESAT6 in a dimeric state, thus improving its cytotoxicity properties. The data presented here provide solid basis for the rational design of upgraded antigens.

Mycobacterium marinum down-regulates miR-148a in macrophages in an EsxA-dependent manner

As a key virulence factor of Mycobacterium tuberculosis, EsxA is not only involved in phagosome rupture, but also functions in stimulation of immune responses in macrophages. Here, we report thatmiR-148a is down-regulated in the macrophages infected with Mycobacterium marinum (Mm). Using the knockout strain Mm∆EsxA/B, recombinant EsxA, EsxB and EsxA/B heterodimer proteins, we provide evidence that down-regulation of miR-148ais dependent on EsxA, and up-regulation of miR-148a reduces Mm intracellular survival. Moreover, up-regulation of miR-148a down-regulates the pro-inflammatory cytokines (e.g. TNF-α and IL-1β) and the TLR4-mediated NF-κB activation. Together, miR-148a may function as an anti-inflammation modulator in responses to mycobacterial infection. Regulation of miR-148a may provide a novel venue in development of therapies in tuberculosis.

Mycobacterium tuberculosis Virulent Factor ESAT-6 Drives Macrophage Differentiation Toward the Pro-inflammatory M1 Phenotype and Subsequently Switches It to the Anti-inflammatory M2 Phenotype

Tuberculosis, a human infectious disease caused by Mycobacterium tuberculosis (M.tb), is still a major cause of morbidity and mortality worldwide. The success of M.tb as a pathogen relies mainly on its ability to divert the host innate immune responses. One way by which M.tb maintains a persistent infection in a "silent" granuloma is to inhibit inflammation and induce an immunoregulatory phenotype in host macrophages (MΦs). However, M.tb effectors governing the switch of MΦs from the pro-inflammatory M1 to the anti-inflammatory M2 phenotype remain to be determined. The Early Secreted Antigenic Target 6 kDa or ESAT-6, has been implicated in the virulence and pathogenesis of tuberculosis. Here, we investigated roles of ESAT-6 in MΦ differentiation and polarization. We found that treatment of human monocytes with ESAT-6 did not interfere with differentiation of M1 MΦs. However, ESAT-6 promoted differentiation of M0 and M2 MΦs toward the M1 phenotype, as indicated by secretion of pro-inflammatory cytokines IL-6, IL-12, and TNF-α, and induction of a typical M1 transcriptional signature. Interestingly, we found that ESAT-6 switched terminal full activation of M1 polarized MΦs to the M2 phenotype. Indeed, in the pro-inflammatory M1 MΦs, ESAT-6 was able to inhibit IL-12 and TNF-α secretion and stimulate that of IL-10. Moreover, gene expression profiling of these cells showed that ESAT-6 induced downregulation of M1 MΦ cell surface molecules CD80 and CD86, transcription factors IRF5 and c-MAF, cytokines IL-12, IL-10, and IL-6, as well as chemokines CXCL10 and CXCL1. Overall, our findings suggest ESAT-6 as being one of the effectors used by M.tb to induce the pro-inflammatory M1 phenotype at the primo-infection; a prerequisite step to promote granuloma formation and subsequently drive the phenotype switch of MΦ polarization from M1 to M2 at a later stage of the infection. Our study improves current knowledge regarding mechanisms of virulence of M.tb and may be helpful to develop novel tools targeting ESAT-6 for a better and more efficient treatment of tuberculosis.

High Antigen Dose Is Detrimental to Post-Exposure Vaccine Protection against Tuberculosis

Mycobacterium tuberculosis (Mtb), the etiologic agent of tuberculosis (TB), causes 1.8M deaths annually. The current vaccine, BCG, has failed to eradicate TB leaving 25% of the world’s population with latent Mtb infection (LTBI), and 5–10% of these people will reactivate and develop active TB. An efficient therapeutic vaccine targeting LTBI could have an enormous impact on global TB incidence, and could be an important aid in fighting multidrug resistance, which is increasing globally. Here we show in a mouse model using the H56 (Ag85B-ESAT-6-Rv2660) TB vaccine candidate that post-exposure, but not preventive, vaccine protection requires low vaccine antigen doses for optimal protection. Loss of protection from high dose post-exposure vaccination was not associated with a loss of overall vaccine response magnitude, but rather with greater differentiation and lower functional avidity of vaccine-specific CD4 T cells. High vaccine antigen dose also led to a decreased ability of vaccine-specific CD4 T cells to home into the Mtb-infected lung parenchyma, a recently discovered important feature of T cell protection in mice. These results underscore the importance of T cell quality rather than magnitude in TB-vaccine protection, and the significant role that antigen dosing plays in vaccine-mediated protection.

Association of ESAT-6/CFP-10-induced IFN-γ, TNF-α and IL-10 with clinical tuberculosis: evidence from cohorts of pulmonary tuberculosis patients, household contacts and community controls in an endemic setting

Mycobacterium tuberculosis (Mtb) early secreted protein antigen 6 (ESAT-6) and culture filtrate protein 10 (CFP-10) are among candidate vaccines against tuberculosis (TB). Results of experimental animal models show that these antigens are associated with induction of strong T cell immunity [interferon (IFN)-γ production], while others report that these proteins as virulent factors involved in pathogenicity of Mtb infection. However, the role of ESAT-6/CFP-10 during natural Mtb infections in humans has not been established. In this paper we present results of a longitudinal study from an Mtb-infected human population from an endemic setting. Whole blood assay was used to determine levels of IFN-γ, tumour necrosis factor (TNF)-α and interleukin (IL)-10 against rESAT-6/CFP-10 in TB patients, household contacts and community controls. The levels of IFN-γ, TNF-α and IL-10 against rESAT-6/CFP-10 at baseline were significantly higher in patients and community controls than in household contacts. In patients, no significant difference was observed in the level of these cytokines before and after chemotherapy whereas, in contacts, the level of these cytokines increased significantly and progressively over time. The study shows that the levels of IFN-γ, TNF-α and IL-10 against rESAT-6/CFP-10 are depressed during Mtb infection or exposure but are elevated during clinical TB. Our findings from a study of naturally infected human population suggest that IFN-γ, TNF-α and IL-10 against rESAT-6/CFP-10 are markers for clinical TB but not for protective immunity.

Early Secreted Antigenic Target of 6-kDa of Mycobacterium tuberculosis Stimulates IL-6 Production by Macrophages through Activation of STAT3

As early secreted antigenic target of 6 kDa (ESAT-6) of Mycobacterium tuberculosis (Mtb) is an essential virulence factor and macrophages are critical for tuberculosis infection and immunity, we studied ESAT-6 stimulated IL-6 production by macrophages. ESAT-6 stimulated significantly higher IL-6 secretion by murine bone marrow derived macrophages (BMDM) compared to culture filtrate protein 10 kDa (CFP10) and antigen 85A. Polymyxin B, an LPS blocker, did not affect ESAT-6 stimulated macrophage IL-6 production. ESAT-6 but not Pam3CSK4 induced IL-6 by TLR2 knockout BMDM. ESAT-6 induced phosphorylation and DNA binding of STAT3 and this was blocked by STAT3 inhibitors but not by rapamycin. STAT3 inhibitors suppressed ESAT-6-induced IL-6 transcription and secretion without affecting cell viability. This was confirmed by silencing STAT3 in macrophages. Blocking neither IL-6Rα/IL-6 nor IL-10 affected ESAT-6-induced STAT3 activation and IL-6 production. Infection of BMDM and human macrophages with Mtb with esat-6 deletion induced diminished STAT3 activation and reduced IL-6 production compared to wild type and esat-6 complemented Mtb strains. Administration of ESAT-6 but not CFP10 induced STAT3 phosphorylation and IL-6 expression in the mouse lungs, consistent with expression of ESAT-6, IL-6 and phosphorylated-STAT3 in Mtb-infected mouse lungs. We conclude that ESAT-6 stimulates macrophage IL-6 production through STAT3 activation.

PPE26 induces TLR2-dependent activation of macrophages and drives Th1-type T-cell immunity by triggering the cross-talk of multiple pathways involved in the host response

The pathophysiological functions and the underlying molecular basis of PE /PPE proteins of M. tuberculosis remain largely unknown. In this study, we focused on the link between PPE26 and host response. We demonstrated that PPE26 can induce extensive inflammatory responses in macrophages through triggering the cross-talk of multiple pathways involved in the host response, as revealed by iTRAQ-based subcellular quantitative proteomics. We observed that PPE26 is able to specifically bind to TLR2 leading to the subsequent activation of MAPKs and NF-κB signaling. PPE26 functionally stimulates macrophage activation by augmenting pro-inflammatory cytokine production (TNF-α, IL-6 and IL-12 p40) and the expression of cell surface markers (CD80, CD86, MHC class I and II). We observed that PPE26-treated macrophages effectively polarizes naïve CD4⁺ T cells to up-regulate CXCR3 expression, and to secrete IFN-γ and IL-2, indicating PPE26 contributes to the Th1 polarization during the immune response. Importantly, rBCG::PPE26 induces stronger antigen-specific TNF-α and IFN-γ activity, and higher levels of the Th1 cytokines TNF-α and IFN-γ comparable to BCG. Moreover, PPE26 effectively induces the reciprocal expansion of effector/memory CD4⁺/CD8⁺ CD44^highCD62L^low T cells in the spleens of mice immunized with this strain. These results suggest that PPE26 may be a TLR2 agonist that stimulates innate immunity and adaptive immunity, indicating that PPE26 is a potential antigen for the rational design of an efficient vaccine against M. tuberculosis.

The early secreted antigenic target of 6 kD of Mycobacterium tuberculosis inhibits the proliferation and differentiation of human peripheral blood CD34+ cells

Abnormalities in hematopoiesis are common in tuberculosis patients and highly prevalent in AIDS patients with tuberculosis coinfection. To explore the potential role of the early secreted antigenic target of 6-kD (ESAT-6) of Mycobacterium tuberculosis (Mtb) in abnormal hematopoiesis in tuberculosis, we studied the effect of ESAT-6 on proliferation and differentiation of in vitro-expanded CD34⁺ cells isolated from the peripheral blood of the healthy donors. ESAT-6 but not control protein antigen 85A (Ag85A) of Mtb inhibited the proliferation of CD34⁺ cell derived peripheral blood stem/progenitor cells (PBSPC) in a dose dependent manner when determined by MTT-assay. ESAT-6 but not Ag85A reduced the number of colony forming cells (CFC) of PBSPC by 60-90% as determined by CFC assay by incubation of CD34⁺ cells in a semi-solid cellulose media in the presence of cytokine cocktail for two weeks. ESAT-6 but not Ag85A increased the percentages of the Annexin-V positive cells and enhanced the cleavage of caspase-3 in PBSPC in a time and dose dependent manner as determined by flow cytometry and Western blot analysis, respectively. ESAT-6 also inhibited murine bone marrow derived non-adherent cell proliferation in response to granulocyte-macrophage colony stimulating factor treatment. We conclude that ESAT-6, an essential virulence factor of Mtb, may contribute to the abnormal hematopoiesis of tuberculosis patients by inhibiting the proliferation and differentiation of hematopoietic cells via apoptosis.

Rational engineering of a virulence gene from Mycobacterium tuberculosis facilitates proteomic analysis of a natural protein N-terminus

Mass spectrometry (MS) for the detection of proteins is an indispensable tool for evaluating the biological processes of the proteome. Proteomics frequently requires proteolysis of proteins into peptide fragments. Proteins can be refractory to ideal proteolysis at the sequence level rendering them difficult to analyze by routine proteomics methods. EsxA (ESAT-6, Early Secreted Antigen, 6kDa) is a major virulence determinant of Mycobacterium tuberculosis, the cause of human tuberculosis. EsxA is routinely used to evaluate mycobacterial virulence in the laboratory and as a biomarker for tuberculosis in humans. The sequence of EsxA hinders deeper MS analysis beyond routine detection. Here we engineer the sequence of EsxA to add desirable tryptic properties aimed at improving complex MS analysis. We demonstrate that EsxA variants are amenable to MS analysis and remain functional in established in vitro and ex vivo assays of Esx-1-function. We provide the first demonstration of molecular engineering to specifically improve MS analysis of individual microbial proteins.

Immunological evaluation of a novel Mycobacterium tuberculosis antigen, Rv3117, absent in Mycobacterium bovis BCG

Tuberculosis (TB) remains a global infectious disease. To investigate the value of a novel Mycobacterium tuberculosis (M. tuberculosis) region of difference 5 (RD5)-encoded antigen, Rv3117, in the development of effective immuno-diagnostics and vaccines against TB, the immune responses to the antigen were examined in human subjects, as well as in C57BL/6 mice. The results showed that Rv3117 was able to evoke specific humoral and cellular immune responses. Consistent with the results from the RD1-encoded antigens, culture filtrate protein 10 kDa (CFP-10) and early secreted antigenic target 6 kDa (ESAT-6), the immunoglobulin G (IgG), IgM and IgA antibody responses to Rv3117 were able to statistically distinguish between the 65 patients with active pulmonary TB and the 59 healthy controls (P<0.01, respectively). In addition, higher levels of Rv3117‑specific interferon-γ (IFN-γ) were observed in immunized C57BL/6 mice than in the negative control mice (P<0.05). Furthermore, high titers of total IgG, IgG1 and IgG2a antibodies were present in the sera from immunized mice, even six weeks subsequent to the immunization. In conclusion, the present results suggested that Rv3117 may be used as a candidate for the development of TB immunodiagnostics and vaccine design.

MprAB regulates the espA operon in Mycobacterium tuberculosis and modulates ESX-1 function and host cytokine response

The ESX-1 secretion system exports the immunomodulatory protein ESAT-6 and other proteins important in the pathogenesis of Mycobacterium tuberculosis. Components and substrates of ESX-1 are encoded at several loci, but the regulation of the encoding genes is only partially understood. In this study, we investigated the role of the MprAB two-component system in the regulation of ESX-1 activity. We determined that MprAB directly regulates the espA gene cluster, a locus necessary for ESX-1 function. Transcript mapping determined that the five genes in the cluster form an operon with two transcriptional start points, and several MprA binding sites were detected in the espA promoter. Expression analyses and promoter constructs indicated that MprAB represses the espA operon. However, the MprAB mutant Rv-D981 secreted lower levels of EspA, ESAT-6, and the ESX-1 substrate EspB than control strains. Secretion of CFP10, which is normally cosecreted with ESAT-6, was similar in Rv-D981 and control strains, further demonstrating aberrant ESX-1 activity in the mutant. ESAT-6 induces proinflammatory cytokines, and macrophages infected with Rv-D981 elicited lower levels of interleukin 1β (IL-1β) and tumor necrosis factor alpha (TNF-α), consistent with the reduced levels of ESAT-6. These findings indicate that MprAB modulates ESX-1 function and reveal a new role for MprAB in host-pathogen interactions.